Two men who held up a jewellery store in Milwaukee, Wisconsin, were themselves robbed as they made their getaway, US police say.

A second pair of robbers pounced on their haul of cash and gems in the street outside, sparking a fight followed by a car chase.

Police pulled over both vehicles and arrested four men, all from Illinois.

But no loot was discovered and police are now searching for more suspects, the Associated Press reports.

Police Lt Thomas Welch said the original robbers were aged 40 and 31 and the two who robbed them in turn were 22 and 27.

No estimate was given of the value of the stolen items.